Some items from this specific schematic: Gasket, Crankcase (nas), Bolt,flange,6x40, Pin,knock 8x12a, Bolt,flange,sh,6x40.
On this parts fiche the Bolt,flange,6x40 is the most specified component.
The most reasonably priced component used on the Z50r 1987 (h) Usa Right Crankcase Cover is the Nut,hex 8mm.